linux-kernel - Re: Corrupt XFS -Filesystems on new Hardware and Kernel

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Date:	Thu, 29 Mar 2007 13:14:07 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Linda Walsh <lkml@...nx.org>, Oliver Joa <oliver@...-a.de>,
	Eric Sandeen <sandeen@...deen.net>,
	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org,
	xfs-oss <xfs@....sgi.com>
Subject: Re: Corrupt XFS -Filesystems on new Hardware and Kernel

On Thu, Mar 29 2007, Jan Kara wrote:
> > Oliver Joa wrote:
> > >>eason or another, xfs has detected a corrupted on-disk inode format 
> > >>which it cannot recognize, and shuts down.
> > ----
> > Oh, one other thing that may not apply in your case, but may.
> > Does your SATA disk support write caching?  Does it support
> > something called a barrier function?  (not real clear on all
> > the ways this can go wrong, but I believe barriers are supposed
> > to guarantee previous data has been fixed on disk (not in write
> > cache).  If the SATA controller issues a reset, it may very well
> > purge the write cache.  Theoretically, I can think of a _possibility_,
> > that the reset disk would purge the write cache and the barrier
> > indicator would tell xfs to resume writing.  From a recent thread
> > on the xfs list, it would appear this could be a "bad" thing (like
> > crossing the streams ala "ghostbusters", but in a data-integrity
> > context).
>   As far as I can remember, barrier does not mean that data is fixed on
> disk. It is only a command that forces all the writes before the barrier
> to be performed before all the writes after the barrier. So this is more
> an ordering restriction than a data integrity thing...

A barrier write guarentees both data before barrier is on disk, as well
as the barrier itself when completion is signalled.

-- 
Jens Axboe

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